I am new to NDK and learning.
I managed to call the native method from java code but don't know how can I compare two jbyte arrays
here is what I have:
jbyte bytes1[] = {48, -126, 1,4};
jbyte bytes2[] = {48, -126, 1,4};
jclass cls = (*env)->GetObjectClass(env, bytes1);
jmethodID mid = (*env)->GetMethodID(env, cls, "equals", "([B)Z");
jboolean isEqual = (*env)->CallBooleanMethod(env, bytes1, mid, bytes2);
I know above code is wrong but is there a correct way of comparing the byte arrays
Use memcmp if you need to compare two jbyte arrays.
#include <string.h>
int memcmp(const void *s1, const void *s2, size_t n);
In your example,
jboolean isEqual = (memcmp(bytes1, bytes2, 4) == 0);
Related
I am new to JNI and trying to muddle my way through. Please can someone point me in the direction to do the following in JNI. I am a bit out of my depth here, Can JNI handle Byte Arrays. Also were is the best places to find JNI examples.
This is the JAVA code I want to convert
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
outputStream.write(key1);
outputStream.write(key2);
byte[] key3 = outputStream.toByteArray();
Thank you in advance
Rob
Here is a literal translation of the Java code you posted:
jclass cls_BAOS = env->FindClass("java/io/ByteArrayOutputStream");
jmethodID ctr_BAOS = env->GetMethodID(cls_BAOS, "<init>", "()V");
jobject baos = env->NewObject(cls_BAOS, ctr_BAOS);
jmethodID mid_BAOS_writeBytes = env->GetMethodID(cls_BAOS, "writeBytes", "([B)V");
env->CallVoidMethod(baos, mid_BAOS_writeBytes, key1);
env->CallVoidMethod(baos, mid_BAOS_writeBytes, key2);
jmethodID mid_BAOS_toByteArray = env->GetMethodID(cls_BAOS, "toByteArray", "()[B");
jbyteArray key3 = (jbytearray)env->CallObjectMethod(baos, mid_BAOS_toByteArray);
And here is an implementation that uses lower-level operations:
jsize key1len = env->GetArrayLength(key1);
jsize key2len = env->GetArrayLength(key2);
jbyteArray key3 = env->NewByteArray(key1+key2);
{
jbyte *key1ptr = env->GetByteArrayElements(key1, nullptr);
env->SetByteArrayRegion(key3, 0, key1len, key1ptr);
env->ReleaseByteArrayElements(key1, key1ptr, JNI_ABORT);
}
{
jbyte *key2ptr = env->GetByteArrayElements(key2, nullptr);
env->SetByteArrayRegion(key3, key1len, key2len, key2ptr);
env->ReleaseByteArrayElements(key2, key2ptr, JNI_ABORT);
}
You could also memcpy both byte arrays to a single C++ array first and then use a single call to SetByteArrayRegion or anything else really, but what's the point? The Java code was simple and readable and all of this JNI code is just adding pointless obfuscation.
Thank you Botje, this is the final code that works.
jclass cls_BAOS = env->FindClass("java/io/ByteArrayOutputStream");
jmethodID ctr_BAOS = env->GetMethodID(cls_BAOS, "<init>", "()V");
jobject baos = env->NewObject(cls_BAOS,ctr_BAOS);
jmethodID mid_BAOS_writeBytes = env->GetMethodID(cls_BAOS, "writeBytes", "([B)V");
env->CallVoidMethod(baos, mid_BAOS_writeBytes, a);
env->CallVoidMethod(baos, mid_BAOS_writeBytes, b);
jmethodID mid_BAOS_toByteArray = env->GetMethodID(cls_BAOS, "toByteArray", "()[B");
jbyteArray key3 = (jbyteArray)env->CallObjectMethod(baos, mid_BAOS_toByteArray);
I want to add C library to my project. lzfse for decode img via apple algorithm.
I have added c files to project
added CmakeLines file:
externalNativeBuild {
cmake {
path "src/main/lzfse/CMakeLists.txt"
version "3.10.2"
}
}
I have written JNI for decode:
JNIEXPORT jint JNICALL
Java_com_android_Decompressor_decode(
JNIEnv* env, jclass cls, jobject src, jobject dst
) {
uint8_t* src_buffer = (*env)->GetDirectBufferAddress(env,src);
const size_t src_size = (const size_t) (*env)->GetDirectBufferCapacity(env, src);
uint8_t* dst_buffer = (*env)->GetDirectBufferAddress(env,dst);
size_t dst_size = (size_t) (*env)->GetDirectBufferCapacity(env, dst);
jlong test = lzfse_decode_buffer(dst_buffer, dst_size, src_buffer, src_size, NULL);
return (jint) test;
}
then I call from kt decode fun:
val buf = ByteBuffer.wrap(byteArray)
val buf_out = ByteBuffer.allocateDirect(byteArray.size *20)
val size= decode(dstArray = buf_out, srcArray = buf)
But
My app just crashes
2020-02-25 20:12:25.717 28603-28603/com.android A/libc: Fatal signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x0 in tid 28603 (), pid 28603 ()
Where did I lose?
Wrapping a ByteArray does not result in a direct buffer (at least on Android).
You will need to call GetByteArrayElements to get a (possibly copied) pointer.
I have fixed the crash! After some time I have decided to publish the working code.
So, the call native c++ from project:
private val dstArray: ByteBuffer = ByteBuffer.allocateDirect(DESTINATION_BUFFER_CAPACITY)
private val srcArray: ByteBuffer = ByteBuffer.allocateDirect(SRC_BUFFER_CAPACITY)
decode(srcArray.put(byteArray), dstArray)
Here instead of:
val buf = ByteBuffer.wrap(byteArray)
val size= decode(dstArray = buf_out, srcArray = buf)
I allocate a direct buffer via ByteBuffer.allocateDirect and put the source array in buffer srcArray.put(byteArray).
Because as #Botje said in his post :
Wrapping a ByteArray does not result in a direct buffer (at least on
Android).
my JNI:
JNIEXPORT JNICALL
Java_com_android_Decompressor_decode(
JNIEnv *env, jclass cls, jobject src, jobject dst
) {
uint8_t *src_buffer = (*env)->GetDirectBufferAddress(env, src);
const size_t src_size = (const size_t) (*env)->GetDirectBufferCapacity(env, src);
uint8_t *dst_buffer = (*env)->GetDirectBufferAddress(env, dst);
size_t dst_size = (size_t) (*env)->GetDirectBufferCapacity(env, dst);
lzfse_decode_buffer(dst_buffer, dst_size, src_buffer, src_size, NULL);
}
So I almost haven't changed JNI.
But in my first code sample, I have found that all works until the line:
//...
return (jint) test;
The line caused the crash.
In my case, I didn't need return value so I rewrite JNI function without return any values, but I think it possible to find where I have failed with the return value.
Thanks, guys who tried to give some help, I hope my post also can be helpful for someone.
I have a problem for parsing float from char in JNI-Android Application.This is my sample data :
0.00618567 0.00224441 0.002006603 0.001813437 0.003761207 -0.001850192 -0.001011893 -0.00342476 0.003790586 0.002385935 0.002647488 0.004411637 0.005938921 0.00698391 0.004522655 0.001524881 -0.002673242 -0.0002569943 -0.002495839 0.00230171 0.000844161 0.006387557 0.008135659 0.005583601 0.002238941 -0.001932641 -0.003518643 -0.0006784072 0.001636732 0.001213515 0.0021472 0.004911256 0.003613603 0.001362842 -0.0002172031 -0.002115535 -0.0002000824 0.001085831 0.003149634 0.003899722 0.004865647 0.002436467 0.0001896242 -0.001678405 -0.001909177 -0.002954236 0.001802054 0.003751467 0.004150682 0.005844797 0.002612064 0.003680898 -0.0005450704 -0.002621638 -0.002253087 0.0005009398 0.004602027 0.003445318 0.00632045 0.002706638 -0.001308871 -0.002082631 -0.001821213 -0.0005696003 0.002069579 0.006264412 0.004593662 0.005836432 0.0009420562 -0.003753015 -0.004050847 -0.001744672 -0.002664186 0.00101941 0.004568859 0.003175343 0.005315124
And this is a type of data vector<float> for hog.setSVMdetector(const vector<float>& detector):
0.05359386f, -0.14721455f, -0.05532170f, 0.05077307f, 0.11547081f, -0.04268804f, 0.04635834f, -0.05468199f, 0.08232084f, 0.10424068f, -0.02294518f, 0.01108519f, 0.01378693f, 0.11193510f, 0.01268418f, 0.08528346f, -0.06309239f, 0.13054633f, 0.08100729f, -0.05209739f, -0.04315529f, 0.09341384f, 0.11035026f, -0.07596218f
this is my sample code .cpp in JNI :
extern "C"
jboolean
Java_com_example_franksyesipangkar_tourguide_CameraPreview_ImageProcessing
(JNIEnv* env, jobject thiz, jint width, jint height, jbyteArray NV21FrameData, jintArray outPixels, jbyteArray b)
{
LOGD("JNIEnv");
//convert jbyteArray to char
jbyte *cmd = env->GetByteArrayElements(b, 0);
LOGD("JNIEnvFeature");
//char * feature = (char *)cmd;
char feature[90600];
memset(feature,0, sizeof(feature));
memcpy(feature, cmd, strlen((char*)cmd));
In this code, a data in char feature which I want to parsing it to data like a type of data hog.setSVMdetector(const vector<float>& detector).So, do you have an idea ?
Maybe this can help you:
#include <iostream>
#include <vector>
#include <strstream>
#include <string>
std::vector<float> parse_delimeted_list_of_numbers(char* line, char delimeter)
{
std::vector<float> vector_of_numbers;
std::istrstream input_stream(line);
std::string text;
float number;
while (std::getline(input_stream, text, delimeter)) {
sscanf_s(text.c_str(), "%f", &number, text.size());
vector_of_numbers.push_back(number);
}
return vector_of_numbers;
}
// A program to test that the above function works well
int _tmain(int argc, _TCHAR* argv[])
{
// auto vector_of_numbers = parse_delimeted_list_of_numbers("234.0, 345, 465, 46456.0",',');
auto vector_of_numbers = parse_delimeted_list_of_numbers("234.0 34 465 46456.0", ' ');
for (auto number : vector_of_numbers)
std::cout << number << "\n";
return 0;
}
I need get byte array from jni to Java.
Ex: I have a byte array byte[] a = {1,2,3,4,5,6}
JNIEXPORT jbyteArray JNICALL Java_com_vn_getArray (JNIEnv *env, jobject obj) {
jbyte[] a = {1,2,3,4,5,6};
return a;
}
I do not know how to return a byte array from jni.
Can someone help me? Please!
In Java, an array is an object. So to hand a byte array from C or C++ over to java you will need to instantiate a jbyteArray, and return that. Instead of a C array. To solve that, see the following code:
JNIEXPORT jbyteArray JNICALL Java_Test_returnArray
(JNIEnv *env, jobject This)
{
jbyte a[] = {1,2,3,4,5,6};
jbyteArray ret = env->NewByteArray(6);
env->SetByteArrayRegion (ret, 0, 6, a);
return ret;
}
Based on this link
I do like that and it's working
JNIEXPORT jbyteArray JNICALL Java_com_vn_getArray(JNIEnv *env, jobject obj) {
jbyte byteUrl[] = {1,2,3,3,4};
int sizeByteUrl = 5;
jbyteArray data = (*env)->NewByteArray(env, sizeByteUrl);
if (data == NULL) {
return NULL; // out of memory error thrown
}
// creat bytes from byteUrl
jbyte *bytes = (*env)->GetByteArrayElements(env, data, 0);
int i;
for (i = 0; i < sizeByteUrl; i++) {
bytes[i] = byteUrl[i];
}
// move from the temp structure to the java structure
(*env)->SetByteArrayRegion(env, data, 0, sizeByteUrl, bytes);
return data;
}
I am trying to understand jni, so I started hacking up hellojni, and I ran into this problem.
My java code looks like this:
short[] buf = new short[16];
Log.d("hello", "before!");
write(buf, 0, 16);
and my C code looks like this:
jint
Java_com_example_hellojni_HelloJni_write(JNIEnv* env, jshortArray buf, jint off, jint len)
{
char debug[1024];
int ii = 0;
jsize cbuflen = (*env)->GetArrayLength(env, buf);
sprintf(debug, "array length: %d", cbuflen);
LOGD(debug);
...
...
The output is:
array length: 1079082088
Why is the array length so big?
Could you show your entire JNI file? You are not declaring the target object in your JNI function. Usually the arguments are JNIEnv* env, jobject javaObject, etc. This means that what you believe is the jshortArray is actually the pointer to a Java object, which would explain the weird results you are getting.